Automatic control for pulverized coal gasification



Oct. 25, 1960 TOSHIO TANIYAMA ETAL 2,957,758

AUTOMATIC CONTROL FOR PULVERIZED COAL GASIFICATION Filed June 18, 1958 AUTOMATIC CONTROL FOR 'PULVERIZED COAL GASIFIC'ATION Toshio Taniyama, Osamu Saeki, and Yoshiichi Karato, Niihama-shi, and Teruyoshi Usamoto, Akita-shi, Japan, assignors to Sumitomo Chemical Company, Ltd., Osaka, Japan, a corporation of Japan Filed June 18, 1958, Ser. No. 742,922

1 Claim. (Cl. 48-63) This invention relates to a process of controlling the temperature of the pulverized coal gasification furnace by automatically adjusting the amount of the raw pulverized coal and the gasification media to be introduced into said furnace. a With respect .to the gasification of pulverized coal in gasification media such as oxygen and water vapor, etc. under floating and suspending conditions, it is well known that the efliciency of gasification and the composition of the produced gas depend upon the ratio of the pulverized coal to the gasification media introduced into the gasification furnace and the gasification temperature, which has an important effect on the efiiciency of the gasification, also depends upon such a ratio. Broadly speaking, these gasification reactions may be classified into the combustion reaction between the pulverized coal and the oxyuited State Pate-MC F gen, and the endothermic gasification reaction between the pulverized coal and the water vapor or the carbon dioxide. According to the chemical equilibrium, the amount of, and the heat for, these reactions may be determined by such factors as the chemical equilibrium constant of the respective reaction, the active surface area of the pulverized coal, the partial pressure of the gasification medium in the furnace and thelike.

In a method of gasifying the pulverized coal by such gasification media as oxygen, water vapor and the like, the decisive factor upon the efficiency of gasification and the gasificationtemperature is a ratio of oxygen to coal. This is evidenced by the result of our tests in the following table for pulverized coal gasification under varied conditions.

TABLE Gasification of raw powdered coal (total calorific value 6,000 kcaL/ kg.) under constant water vapor-coal ratio (0.4 kg./ kg.)

1 2,957,758 Patented Oct. 25, 1 960 vice at the entry of the burner, and automatically controlling the temperature of the gasification furnace by adjusting the amount of the oxygen in said other system than the one for transferring the coal. In each main system of transferring and introducing the pulverized coal and the gasification medium into the furnace, the amounts of the pulverized coal and the gasification medium supplied can be adjusted to a constant ratio by means of a device of maintaining the amounts of pulverized coal, oxygen and water vapor at constant values, which device is connected with an instrument for measuring the rate of supplying pulverized coal in terms of mass, while the amount of oxygen supplied from other system can be passed through, and automatically adjusted by, an instrument for measuring the temperature of the future.

In order to introduce the pulverized coal and the gasification medium into the pulverized coal gasification furnace, a method is usually employed which comprises mixing them at a constant quantitative ratio before they are supplied into the furnace from a number of systems each of which has one burner therein. When the ratios of the amounts of pulverized coal and gasification medium supplied are not uniform with respect to each supplying system, not only'each flame temperature inside the furnace but also the mixing of the pulverized coal and the gasification medium becomes so irregular that the gasification temperature fluctuates and thereby decreases the efliciency of the gasification and varies the composition of the produced gas. The cause of this irregularity of the supplying ratio of pulverized coal and the gasification medium in each system is the qualitative fluctuation of the raw pulverized coal, e.'g., calorific value, moisture content, ash content, available hydrogen content and the like, and the qualitative fluctuation of the gasification medium, e.g., purity of oxygen, temperature, pressure, moisture content and the like or the temperature and pressure of the water vapor and the like, which can not be overcome by the mere quantitative control as described above. Fluctuation of the gasification temperature, which is due to the above qualitative fluctuation, can be reduced to the minimum by automatic adjustment of the amount of oxygen supplied from the other source.

In the present method of the invention, a major part, e.g., 8090%, of the amount of oxygen required for gasification of a determined amount of pulverized coal introduced into the furnace may be supplied with the coal Test Number I II III IV V Oxygen-coal ratio (m. /kg.) 0.45 0.50 0.55 0.60 .0. 65 Produced gas (OOHr)- coal ratio (mfi/kg.) 1. 10 1. 28 1. 37 1. 25 1. 14 Produced gas temperature C02 in produced gas (percent) 16. 5 16. 0 16. 5 19. 0 21. 5

Accordingly, the control of the gasification temperature can be made by adjusting the ratio of oxygen-coal.

This invention is a process of automatic control for pulverized coal gasification wherein the pulverized coal is gasified by such gasification media as oxygen, water vapor and the like under floating and suspending conditions, which comprises supplying the total amount of oxygen required for gasification from the oxygen which transfers the coal from the feeding device to the burner and from the oxygen in other system which is mixed from the main system, while a minor part, e.g., 20-10%, of the necessary amount of oxygen may be fed from another system. In this case, the major part of the amount of oxygen supplied from the main system is always kept at a constant value, while the minor part of the amount of oxygen supplied from the other system is allowed to automatically change responding to the temperature change inside the furnace caused by the qualitative fluctuations of the pulverized coal and the gasification media.

In order to obtain a maximum efficiency of gasification, the ratio of oxygen to coal may vary with a range between 0.5 and 0.55 m. Under such gasification conditions, the fluctuation of the gasification temperature is 6" -7 C. at 1200 C. for the fluctuation of 1% of the oxygen-coal ratio. Lln this connection, the practical accuracy of measuring the gasification temperature is 5 C. at 1200 C. Accordingly, the temperature inside the furnace can be controlled by automatically adjusting the amount of oxygen in the other system to 1% in terms of the ratio of oxygen to coal in association with the temperature measuring device. As for the in cidental fluctuations based upon the qualitative fluctuations of the raw pulverized coal and the gasification media, .there is a fluctuation, in addition to that of the gasificationtemperature, of the composition of the produced gas. In view of the fact that the fluctuation of the carbon dioxide content in the produced gas depends upon the ratio of Water vapor to coal, this problem can also be overcome by automatically adjusting the amount of water vapor introduced in a similar manner to the adjustment of oxygen in association with a measuring device for the variation of the carbon dioxide content in the produced gas so that the composition of the produced gas be maintained at a constant value.

In order that the present invention may be fully understood it will now be described with reference to the accompanying drawing which schematically illustrates one embodiment of the present invention.

EXAMPLE In the drawing, an arrangement of gasification of pulverized coal having two supplying systems for the raw material and the gasification media is shown, the thick solid lines indicating the passageways for coal, oxygen and water vapor. The numerical references, 1, 2 and 2 3 and 3 4, and 5 and 5 are respectively the body of the gasification furnace, the burner for the raw material and the gasification media, the feeder for the pulverized coal, the main pipe for withdrawing the generated gas and the detector of the supplying rate (mass proportion) of the pulverized coal into the furnace. The rate of supplying the pulverized coal may be kept at a constant level by the automatic operation of the adjustment valves 7 and 7 through the adjustment meters 6 and 6 The set index of these meters 6 and 6 may be operated in a unitary manner from a remote place, and this can be accomplished by a manual operation of the pneumatic adjustment valve 8. In addition are shown the inlet pipes 9 and 9 for oxygen of the main system, the inlet pipes 10 and 10 for water vapor'of the main system, the inlet pipe 11 for oxygen of the other system and the inlet pipe 12 for water vapor of the other system. The flow adjustment meters 171, 18 191, 201 and 172, 182, 19 202 are connected pneumatically or electrically with the flow detectors 13 14 15 16 and 13 14 15 16 for oxygen and water vapor introduced into the furnace, which meters are in turn connected pneumatically with the flow adjustment valves 21 22 23 24 and 21 22 23 24 and the like. Consequently, when the amounts of these flows fluctuate for some reason, they can immediately be detected by the corresponding flow detectors so as to recover the original states. Moreover, the set indices of the adjustment meters 17 18 and 17 and 18 for the amounts of oxygen and water vapor of the main system may be operated pneumatically and electrically in such a manner that they are in a constant relation with the indices of the adjusting meters 6 and 6 for supplying coal so that the ratios of oxygencoal and water vapor-coal be maintained at constant values. The adjustment of these ratios can be made automatically.

The amounts of oxygen and Water vapor which may be proportionally adjusted directly with respect to the amount of coal supplied are at constant values between 80 and 90% of the total amount of oxygen and that of water vapor fed to the gasification furnace. The re maining amount, i.e. 10* to may be supplied from the other systems 11 and 12 as the one for adjustment of the gasification temperature and the carbon dioxide content in the produced gas.

The reference number 25 shows the detecting point of the temperature adjustment meter 26 for measuring the gasification temperature at the exit of the gasification furnace. If the value changes, it can be restored to the original state by the unitary operation of the set indices of the oxygen flow adjustment meters 19 and 19 of the other systems by means of the temperature adjustment meter 26. Alternatively, a unitary and direct operation of the oxygen flow adjustment valves 23 and 23 may be allowed by means. of. the temperature adjustment meter 26 without the necessity of establishing the fiow adjustment meters 19 and 19 Also the reference number 27 shows the detecting point of the carbon dioxide adjustment meter 28 for measuring the content of carbon dioxide in the produced gas. If the value changes, it can be restored to the original state by the unitary operation of the set indices the Water vapor flow adjustment meters 20 and 20 of the other systems by means of the carbon dioxide adjustment meter 28. Alternatively, a unitary and direct operation of the water vapor fiow adjustment valves 24 and 24 may be allowed by means of the carbon dioxide adjustment meter 28 without the necessity of establishing the flow adjustment meters 20 and 20 In the practice of the present invention, one of the optimum methods to charge the raw gasification material and gasification media such as powdered coal, oxygen, water vapor and the like into the gasification furnace is as follows. In each system for supplying the raw material, the pulverized coal is caused to float in the stream of oxygen equivalent to to of the total amount of oxygen. Then the water vapor in the amount equivalent to 80 to 90% of the total amount of the water vapor added is mixed into the pulverized coal-oxygen stream immediately before it is introduced into the gasification furnace. In this case it is obvious that the ratios of oxygen-coal and water vapor-coal may be adjusted automatically and independently in each system. Meanwhile, the remaining oxygen equivalent 10- 20% of the total amount of oxygen and the remaining water vapor equivalent to 10-20% of the total amount of water vapor added for adjustment of the gasification temperature and of the carbon dioxide content in the pro duced gas, respectively, are uniformly distributed and mixed in each system. Then it is combined into the mixed pulverized coal oxygen water vapor stream inside the burner therefor, and introduced into the gasification furnace as an intimate mixture.

In the floating and suspending type operation of the gasification furnace, the application of the present invention is described below as compared with the conventional manual and separate adjustment with respect to the variation of the ratio of each raw material and the variation of the efiiciency of gasification, etc. As for the rate of supplying pulverized coal, it is caused to fluctuate with the variation of the height of coal accumulated in the storage tank or of the difference of pressure between the entry and the exit of the feeder, since the pulverized coal has a semi-fluid character even if the rotating speed of the feeder is kept constant. In this case it may be observed that the practical range of variation is :10%. It may also be observed that the feeding rate of the pulverized coal fluctuates by the order of :5% at the same rotating speed of the feeder with the variation of moisture content and the particle size of the coal. It has been found that when this feeding rate is measured by the flow weigher or the radio isotope now in practical use, the limit of error or sensitivity is about *-12%, and that when the Bayer variable speed reduction unit or the U5. variable speed motor is operated automatically by this feeding rate detector through the adjustment meter, the range of variation of the feeding rate is :S%. In the latter case, the delay of the time for controlling is great as there is a large amount of pulverized coal accumulated between the detector and the feeder.

Moreover, such automatic control of the feeding rate is made as to the weight of the coal, and it is impossible to control the substantial amount which responds to the qualitative change of the pulverized coal or the changes of the composition and the calorific value of the coal. For example, this qualitative change incurs the variation of calorific value in 12.5% or kcal. per 6,000 kcal. Also the moisture content and the ash content of the pulverized coal will fluctuate within the range of 1.5 to 3.5% by weight and 20 to 23% by weight, respectively.

According to the detected value of the feeding rate, the flowing amounts of oxygen and water vapor are automatically controlled by the unitary operation of the set indices of the corresponding adjustment meters such that the ratios of oxygen to coal and water vapor to coal become constant. In this point, the ranges of variation of the ratios of oxygen-coal and water vapor to coal are 12% so long as the qualitative conditions, for example, the purity, temperature, moisture content, and pressure of oxygen as well as the temperature and pressure of water vapor, are kept contant. Practically speaking, however, the purity of oxygen may vary by the order of :L-1% while the temperature may also vary by C. between day and night, which will cause the change in volume of about 3%. The variation of the moisture content will cause the volumetric change of about 1%.

Accordingly, the control of the substantial, absolute amount is practically impossible for the described reason even if the ratios of oxygen to coal and water vapor to coal are controlled with respect to the apparent flowing amounts thereof. However, in order to make as uniform as possible the temperature of the flame caused by the injection of each nozzle, it is necessary to control the ratios of oxygen to coal and water vapor to coal to as constant a value as possible in each independent system of supplying the pulverized coal.

This is the reason Why the amounts of oxygen and water vapor added in the coal supplying system should be 80 to 90% of the total while the remaining 20 to 10% should be supplied from the other system to the gasification furnace, wherein the control of the amounts supplied is made by the unitary operation through the detectoradjustment meters for the temperature of the gasification furnace and for the carbon dioxide content in the produced gas, thereby distributing the amount uniformly to each burner.

Since the limit of error and sensitivity of the pyrometer now in use for detecting the temperature inside the gasification furnace is i-S" C., it is possible to control 1% of the oxygen-coal ratio easily and accurately from the relation of the ratio with the gasification temperature as described.

The limit of error and sensitivity in detecting carbon dioxide in the produced gas is i0.2% in a method using infrared light. Consequently, it is also possible to control 2.5% of the water vapor-coal ratio easily and accurately from the relation of the ratio with the carbon dioxide content in the produced gas.

According to the method of the present invention, therefore, it is possible to maintain the accurate and constant conditions of the temperature and the composition of gas against the qualitative variation of the raw pulverized coal as well as of the gasification media, i.e. oxygen and water vapor, which condition can not be attained by the mere control of the ratio by the flow meter.

The beneficial eifects of the present invention is obvious from the following table which shows the results of the comparison of the conventional manual control with the automatic control of the present invention with respect to the variation limits of the rate of gas produced, the rate of consumption for the effective gas (CO +H of the raw material, oxygen and Water vapor, the gasification temperature and the carbon dioxide content of the produced gas.

What is claimed is:

Apparatus for the gasification of pulverized coal comprising a furnace, a pulverized coal supply, a primary oxygen supply, a line connecting said oxygen supply to said furnace, a coal rate detector connecting said coal supply to said line, a control valve connected to said oxygen supply, a coal control connected to the coal supply and responsive to said coal rate detector for controlling rate of coal supply, an oxygen flow detector and flow adjustment valve in said line, an oxygen flow adjustment meter coupled to the oxygen flow detector and coal control to effect a supply of to of oxygen necessary for a partial combustion of the coal, a steam supply, a steam detector and flow control coupling the steam supply to said furnace in operative association with said line, a meter coupled to the steam supply and said coal control to provide steam as required by the flow of said coal, a secondary oxygen supply, a secondary flow detector and adjustment valve coupling the secondary supply to said furnace for the supply of secondary oxygen in an amount of about 10 to 20% of the oxygen required for said partial combustion and a temperature detector operatively associated with said furnace and coupled to said secondary supply to control the flow of secondary oxygen to said furnace.

References Cited in the file of this patent UNITED STATES PATENTS 2,563,460 Faber Aug. 7, 1951 2,650,154 Anderson Aug. 25, 1953 2,664,402 Crompans Dec. 29, 1953 2,667,410 Pierce Jan. 26, 1954 2,683,656 Mayland July 13, 1954 2,701,755 Strausser Feb. 8, 1955 2,702,238 Hays Feb. 15, 1955 2,716,598 Moses Aug. 30, 1955 2,769,693 Bearer Nov. 6, 1956 

